In the manufacturing process of a semiconductor substrate or the like, a plasma treatment apparatus for applying a surface process to such a substrate by using plasma may be used. As a plasma treatment apparatus, for example, an apparatus for applying a Chemical Vapor Deposition (CVD) process is known. Among plasma treatment apparatuses, a parallel plate type plasma treatment apparatus is widely used because it is excellent in process evenness and the apparatus structure is relatively simple.
A plasma treatment apparatus is provided with an electrode for turning a material gas and the like into plasma when a high frequency electricity is supplied into a vacuum container in which a surface process for a substrate is performed.
There is a case where a high frequency power source and the electrode are electrically connected by inserting a power feeding bar which leads to the electrode, to a socket, in order to supply a high frequency electricity to the vacuum container. This socket has a multi-surface contact arranged thereinside, and is provided at, for example, the output portion of an impedance matching device to become capable of transmitting a high frequency electricity sent from the high frequency power source to the power feeding bar. The multi-surface contact has, for example, a ring shape, and has multiple contact pins whose surface has a sphere shape. These contact pins are biased toward the inside of the socket by springs. When the power feeding bar is inserted into this socket, these contact pins electrically connect the power feeding bar and the socket by elastically holding the power feeding bar.
By arranging, as described above, the multi-surface contact at the electric contact interface between the socket provided at the output portion of the impedance matching device and the power feeding bar, attempts have been made to secure a predetermined effective contact area and contact pressure.
There is a method which employs a matching box, for electrically connecting the power feeding bar, which leads to the electrode, and an external electric circuit The matching box is fixed on the external wall of the vacuum container, and has contact pins in the interior of the vacuum container. The power feeding bar connected to the electrode is to be connected to the contact pins. An external power source is to be connected to the contact pins via an external terminal. In some case, the contact pins may be fitted into the power feeding bar. In this case, according to a conventional manner, as shown in FIG. 8 for example, contact pins 70a for connecting a matching box 70 and a power feeding bar 71 are initially provided in a protruded manner on the external portion of the matching box 70. In attaching the power feeding bar 71 to the matching box 70, the contact pins 70a are firstly fitted into fitting holes 71a provided to the power feeding bar 71, and then the body of the matching box 70 is screwed and fixed on a frame or the like provided on the external wall of the vacuum container.
The impedance matching device and the matching box accommodating the impedance matching device are attached to and detached from the plasma treatment apparatus for maintenance sake or modification of electric characteristics. The attaching and detaching actions cause a problem that the contact area of the power feeding bar and multi-surface contact changes to cause contact resistance variation. Since the contact resistance variation changes the electric characteristics of the transmission path of high frequency electricity, plasma becomes ununiform and the loss due to resistance components increases.
In order to stabilize the contact resistance between the power feeding bar and the socket, it is preferred that a plating process be applied to the surface of the power feeding bar. However, in some case, the power feeding bar is directly connected to the electrode. In this case, the plating process is difficult to apply from the structural aspect. Further, portions being in contact with a vacuum area could not be plated because plating could be a cause for contamination.
Furthermore, in a case where the contact pins protuberantly provided on the matching box are to be connected to the power feeding bar by fitting the contact pins into the power feeding bar, the fitting of the contact pins must be carried out earlier than the screwing of the matching box. Since the matching box weighs considerably, as much as approximately 10 Kg to 20 Kg in general, it has been difficult to precisely insert the contact pins into the power feeding bar. Moreover, a strong impact is applied to the power feeding bar unless the heavy matching box is appropriately supported until the matching box is screwed. Because of this, there has been a problem that the contact pins connecting the matching box and the power feeding bar and the power feeding bar itself are easily destroyed